java.nio.charset.Charset Maven / Gradle / Ivy
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package java.nio.charset;
//import java.nio.ByteBuffer;
//import java.nio.CharBuffer;
import java.util.Collections;
import java.util.HashSet;
import java.util.Iterator;
import java.util.Locale;
import java.util.Map;
import java.util.Set;
import java.util.SortedMap;
import java.util.TreeMap;
/**
* A named mapping between sequences of sixteen-bit Unicode code units and sequences of
* bytes. This class defines methods for creating decoders and encoders and
* for retrieving the various names associated with a charset. Instances of
* this class are immutable.
*
* This class also defines static methods for testing whether a particular
* charset is supported, for locating charset instances by name, and for
* constructing a map that contains every charset for which support is
* available in the current Java virtual machine. Support for new charsets can
* be added via the service-provider interface defined in the {@link
* java.nio.charset.spi.CharsetProvider} class.
*
*
All of the methods defined in this class are safe for use by multiple
* concurrent threads.
*
*
*
* Charset names
*
* Charsets are named by strings composed of the following characters:
*
*
*
* - The uppercase letters 'A' through 'Z'
* ('\u0041' through '\u005a'),
*
*
- The lowercase letters 'a' through 'z'
* ('\u0061' through '\u007a'),
*
*
- The digits '0' through '9'
* ('\u0030' through '\u0039'),
*
*
- The dash character '-'
* ('\u002d', HYPHEN-MINUS),
*
*
- The plus character '+'
* ('\u002b', PLUS SIGN),
*
*
- The period character '.'
* ('\u002e', FULL STOP),
*
*
- The colon character ':'
* ('\u003a', COLON), and
*
*
- The underscore character '_'
* ('\u005f', LOW LINE).
*
*
*
* A charset name must begin with either a letter or a digit. The empty string
* is not a legal charset name. Charset names are not case-sensitive; that is,
* case is always ignored when comparing charset names. Charset names
* generally follow the conventions documented in RFC 2278: IANA Charset
* Registration Procedures.
*
*
Every charset has a canonical name and may also have one or more
* aliases. The canonical name is returned by the {@link #name() name} method
* of this class. Canonical names are, by convention, usually in upper case.
* The aliases of a charset are returned by the {@link #aliases() aliases}
* method.
*
*
*
* Some charsets have an historical name that is defined for
* compatibility with previous versions of the Java platform. A charset's
* historical name is either its canonical name or one of its aliases. The
* historical name is returned by the getEncoding() methods of the
* {@link java.io.InputStreamReader#getEncoding InputStreamReader} and {@link
* java.io.OutputStreamWriter#getEncoding OutputStreamWriter} classes.
*
*
*
* If a charset listed in the IANA Charset
* Registry is supported by an implementation of the Java platform then
* its canonical name must be the name listed in the registry. Many charsets
* are given more than one name in the registry, in which case the registry
* identifies one of the names as MIME-preferred. If a charset has more
* than one registry name then its canonical name must be the MIME-preferred
* name and the other names in the registry must be valid aliases. If a
* supported charset is not listed in the IANA registry then its canonical name
* must begin with one of the strings "X-" or "x-".
*
*
The IANA charset registry does change over time, and so the canonical
* name and the aliases of a particular charset may also change over time. To
* ensure compatibility it is recommended that no alias ever be removed from a
* charset, and that if the canonical name of a charset is changed then its
* previous canonical name be made into an alias.
*
*
*
Standard charsets
*
*
*
* Every implementation of the Java platform is required to support the
* following standard charsets. Consult the release documentation for your
* implementation to see if any other charsets are supported. The behavior
* of such optional charsets may differ between implementations.
*
*
* Charset
Description
US-ASCII
* Seven-bit ASCII, a.k.a. ISO646-US,
* a.k.a. the Basic Latin block of the Unicode character set ISO-8859-1
* ISO Latin Alphabet No. 1, a.k.a. ISO-LATIN-1 UTF-8
* Eight-bit UCS Transformation Format UTF-16BE
* Sixteen-bit UCS Transformation Format,
* big-endian byte order UTF-16LE
* Sixteen-bit UCS Transformation Format,
* little-endian byte order UTF-16
* Sixteen-bit UCS Transformation Format,
* byte order identified by an optional byte-order mark
*
* The UTF-8 charset is specified by RFC 2279; the
* transformation format upon which it is based is specified in
* Amendment 2 of ISO 10646-1 and is also described in the Unicode
* Standard.
*
*
The UTF-16 charsets are specified by RFC 2781; the
* transformation formats upon which they are based are specified in
* Amendment 1 of ISO 10646-1 and are also described in the Unicode
* Standard.
*
*
The UTF-16 charsets use sixteen-bit quantities and are
* therefore sensitive to byte order. In these encodings the byte order of a
* stream may be indicated by an initial byte-order mark represented by
* the Unicode character '\uFEFF'. Byte-order marks are handled
* as follows:
*
*
*
* When decoding, the UTF-16BE and UTF-16LE
* charsets interpret the initial byte-order marks as a ZERO-WIDTH
* NON-BREAKING SPACE; when encoding, they do not write
* byte-order marks.
When decoding, the UTF-16 charset interprets the
* byte-order mark at the beginning of the input stream to indicate the
* byte-order of the stream but defaults to big-endian if there is no
* byte-order mark; when encoding, it uses big-endian byte order and writes
* a big-endian byte-order mark.
*
* In any case, byte order marks occuring after the first element of an
* input sequence are not omitted since the same code is used to represent
* ZERO-WIDTH NON-BREAKING SPACE.
*
* Every instance of the Java virtual machine has a default charset, which
* may or may not be one of the standard charsets. The default charset is
* determined during virtual-machine startup and typically depends upon the
* locale and charset being used by the underlying operating system.
*
* The {@link StandardCharsets} class defines constants for each of the
* standard charsets.
*
*
Terminology
*
* The name of this class is taken from the terms used in
* RFC 2278.
* In that document a charset is defined as the combination of
* one or more coded character sets and a character-encoding scheme.
* (This definition is confusing; some other software systems define
* charset as a synonym for coded character set.)
*
*
A coded character set is a mapping between a set of abstract
* characters and a set of integers. US-ASCII, ISO 8859-1,
* JIS X 0201, and Unicode are examples of coded character sets.
*
*
Some standards have defined a character set to be simply a
* set of abstract characters without an associated assigned numbering.
* An alphabet is an example of such a character set. However, the subtle
* distinction between character set and coded character set
* is rarely used in practice; the former has become a short form for the
* latter, including in the Java API specification.
*
*
A character-encoding scheme is a mapping between one or more
* coded character sets and a set of octet (eight-bit byte) sequences.
* UTF-8, UTF-16, ISO 2022, and EUC are examples of
* character-encoding schemes. Encoding schemes are often associated with
* a particular coded character set; UTF-8, for example, is used only to
* encode Unicode. Some schemes, however, are associated with multiple
* coded character sets; EUC, for example, can be used to encode
* characters in a variety of Asian coded character sets.
*
*
When a coded character set is used exclusively with a single
* character-encoding scheme then the corresponding charset is usually
* named for the coded character set; otherwise a charset is usually named
* for the encoding scheme and, possibly, the locale of the coded
* character sets that it supports. Hence US-ASCII is both the
* name of a coded character set and of the charset that encodes it, while
* EUC-JP is the name of the charset that encodes the
* JIS X 0201, JIS X 0208, and JIS X 0212
* coded character sets for the Japanese language.
*
*
The native character encoding of the Java programming language is
* UTF-16. A charset in the Java platform therefore defines a mapping
* between sequences of sixteen-bit UTF-16 code units (that is, sequences
* of chars) and sequences of bytes.
*
*
* @author Mark Reinhold
* @author JSR-51 Expert Group
* @since 1.4
*
* @see CharsetDecoder
* @see CharsetEncoder
* @see java.nio.charset.spi.CharsetProvider
* @see java.lang.Character
*/
public abstract class Charset
implements Comparable
{
/* -- Static methods -- */
private static volatile String bugLevel = null;
/**
* Checks that the given string is a legal charset name.
*
* @param s
* A purported charset name
*
* @throws IllegalCharsetNameException
* If the given name is not a legal charset name
*/
private static void checkName(String s) {
int n = s.length();
if (n == 0)
throw new IllegalCharsetNameException(s);
for (int i = 0; i < n; i++) {
char c = s.charAt(i);
if (c >= 'A' && c <= 'Z') continue;
if (c >= 'a' && c <= 'z') continue;
if (c >= '0' && c <= '9') continue;
if (c == '-' && i != 0) continue;
if (c == '+' && i != 0) continue;
if (c == ':' && i != 0) continue;
if (c == '_' && i != 0) continue;
if (c == '.' && i != 0) continue;
throw new IllegalCharsetNameException(s);
}
}
// Cache of the most-recently-returned charsets,
// along with the names that were used to find them
//
private static volatile Object[] cache1 = null; // "Level 1" cache
private static volatile Object[] cache2 = null; // "Level 2" cache
private static void cache(String charsetName, Charset cs) {
cache2 = cache1;
cache1 = new Object[] { charsetName, cs };
}
// Creates an iterator that walks over the available providers, ignoring
// those whose lookup or instantiation causes a security exception to be
// thrown. Should be invoked with full privileges.
//
private static Iterator providers() {
return Collections.emptyIterator();
}
// Thread-local gate to prevent recursive provider lookups
private static ThreadLocal gate = new ThreadLocal();
private static Charset lookupViaProviders(final String charsetName) {
return null;
}
/* The extended set of charsets */
private static Object extendedProviderLock = new Object();
private static boolean extendedProviderProbed = false;
private static Charset lookupExtendedCharset(String charsetName) {
return null;
}
private static Charset lookup(String charsetName) {
if (charsetName == null)
throw new IllegalArgumentException("Null charset name");
Object[] a;
if ((a = cache1) != null && charsetName.equals(a[0]))
return (Charset)a[1];
// We expect most programs to use one Charset repeatedly.
// We convey a hint to this effect to the VM by putting the
// level 1 cache miss code in a separate method.
return lookup2(charsetName);
}
private static Charset lookup2(String charsetName) {
Object[] a;
if ((a = cache2) != null && charsetName.equals(a[0])) {
cache2 = cache1;
cache1 = a;
return (Charset)a[1];
}
/* Only need to check the name if we didn't find a charset for it */
checkName(charsetName);
return null;
}
/**
* Tells whether the named charset is supported.
*
* @param charsetName
* The name of the requested charset; may be either
* a canonical name or an alias
*
* @return true if, and only if, support for the named charset
* is available in the current Java virtual machine
*
* @throws IllegalCharsetNameException
* If the given charset name is illegal
*
* @throws IllegalArgumentException
* If the given charsetName is null
*/
public static boolean isSupported(String charsetName) {
return (lookup(charsetName) != null);
}
/**
* Returns a charset object for the named charset.
*
* @param charsetName
* The name of the requested charset; may be either
* a canonical name or an alias
*
* @return A charset object for the named charset
*
* @throws IllegalCharsetNameException
* If the given charset name is illegal
*
* @throws IllegalArgumentException
* If the given charsetName is null
*
* @throws UnsupportedCharsetException
* If no support for the named charset is available
* in this instance of the Java virtual machine
*/
public static Charset forName(String charsetName) {
Charset cs = lookup(charsetName);
if (cs != null)
return cs;
throw new UnsupportedCharsetException(charsetName);
}
// Fold charsets from the given iterator into the given map, ignoring
// charsets whose names already have entries in the map.
//
private static void put(Iterator i, Map m) {
while (i.hasNext()) {
Charset cs = i.next();
if (!m.containsKey(cs.name()))
m.put(cs.name(), cs);
}
}
/**
* Constructs a sorted map from canonical charset names to charset objects.
*
* The map returned by this method will have one entry for each charset
* for which support is available in the current Java virtual machine. If
* two or more supported charsets have the same canonical name then the
* resulting map will contain just one of them; which one it will contain
* is not specified.
*
* The invocation of this method, and the subsequent use of the
* resulting map, may cause time-consuming disk or network I/O operations
* to occur. This method is provided for applications that need to
* enumerate all of the available charsets, for example to allow user
* charset selection. This method is not used by the {@link #forName
* forName} method, which instead employs an efficient incremental lookup
* algorithm.
*
*
This method may return different results at different times if new
* charset providers are dynamically made available to the current Java
* virtual machine. In the absence of such changes, the charsets returned
* by this method are exactly those that can be retrieved via the {@link
* #forName forName} method.
*
* @return An immutable, case-insensitive map from canonical charset names
* to charset objects
*/
public static SortedMap availableCharsets() {
TreeMap tm = new TreeMap();
tm.put("UTF-8", Charset.defaultCharset());
return tm;
}
private static volatile Charset defaultCharset;
/**
* Returns the default charset of this Java virtual machine.
*
* The default charset is determined during virtual-machine startup and
* typically depends upon the locale and charset of the underlying
* operating system.
*
* @return A charset object for the default charset
*
* @since 1.5
*/
public static Charset defaultCharset() {
if (defaultCharset == null) {
defaultCharset = forName("UTF-8");
}
return defaultCharset;
}
/* -- Instance fields and methods -- */
private final String name; // tickles a bug in oldjavac
private final String[] aliases; // tickles a bug in oldjavac
private Set aliasSet = null;
/**
* Initializes a new charset with the given canonical name and alias
* set.
*
* @param canonicalName
* The canonical name of this charset
*
* @param aliases
* An array of this charset's aliases, or null if it has no aliases
*
* @throws IllegalCharsetNameException
* If the canonical name or any of the aliases are illegal
*/
protected Charset(String canonicalName, String[] aliases) {
checkName(canonicalName);
String[] as = (aliases == null) ? new String[0] : aliases;
for (int i = 0; i < as.length; i++)
checkName(as[i]);
this.name = canonicalName;
this.aliases = as;
}
/**
* Returns this charset's canonical name.
*
* @return The canonical name of this charset
*/
public final String name() {
return name;
}
/**
* Returns a set containing this charset's aliases.
*
* @return An immutable set of this charset's aliases
*/
public final Set aliases() {
if (aliasSet != null)
return aliasSet;
int n = aliases.length;
HashSet hs = new HashSet(n);
for (int i = 0; i < n; i++)
hs.add(aliases[i]);
aliasSet = Collections.unmodifiableSet(hs);
return aliasSet;
}
/**
* Returns this charset's human-readable name for the default locale.
*
* The default implementation of this method simply returns this
* charset's canonical name. Concrete subclasses of this class may
* override this method in order to provide a localized display name.
*
* @return The display name of this charset in the default locale
*/
public String displayName() {
return name;
}
/**
* Tells whether or not this charset is registered in the IANA Charset
* Registry.
*
* @return true if, and only if, this charset is known by its
* implementor to be registered with the IANA
*/
public final boolean isRegistered() {
return !name.startsWith("X-") && !name.startsWith("x-");
}
/**
* Returns this charset's human-readable name for the given locale.
*
* The default implementation of this method simply returns this
* charset's canonical name. Concrete subclasses of this class may
* override this method in order to provide a localized display name.
*
* @param locale
* The locale for which the display name is to be retrieved
*
* @return The display name of this charset in the given locale
*/
public String displayName(Locale locale) {
return name;
}
/**
* Tells whether or not this charset contains the given charset.
*
* A charset C is said to contain a charset D if,
* and only if, every character representable in D is also
* representable in C. If this relationship holds then it is
* guaranteed that every string that can be encoded in D can also be
* encoded in C without performing any replacements.
*
*
That C contains D does not imply that each character
* representable in C by a particular byte sequence is represented
* in D by the same byte sequence, although sometimes this is the
* case.
*
*
Every charset contains itself.
*
*
This method computes an approximation of the containment relation:
* If it returns true then the given charset is known to be
* contained by this charset; if it returns false, however, then
* it is not necessarily the case that the given charset is not contained
* in this charset.
*
* @return true if the given charset is contained in this charset
*/
public abstract boolean contains(Charset cs);
/**
* Constructs a new decoder for this charset.
*
* @return A new decoder for this charset
*/
public abstract CharsetDecoder newDecoder();
/**
* Constructs a new encoder for this charset.
*
* @return A new encoder for this charset
*
* @throws UnsupportedOperationException
* If this charset does not support encoding
*/
public abstract CharsetEncoder newEncoder();
/**
* Tells whether or not this charset supports encoding.
*
* Nearly all charsets support encoding. The primary exceptions are
* special-purpose auto-detect charsets whose decoders can determine
* which of several possible encoding schemes is in use by examining the
* input byte sequence. Such charsets do not support encoding because
* there is no way to determine which encoding should be used on output.
* Implementations of such charsets should override this method to return
* false.
*
* @return true if, and only if, this charset supports encoding
*/
public boolean canEncode() {
return true;
}
/**
* Convenience method that decodes bytes in this charset into Unicode
* characters.
*
* An invocation of this method upon a charset cs returns the
* same result as the expression
*
*
* cs.newDecoder()
* .onMalformedInput(CodingErrorAction.REPLACE)
* .onUnmappableCharacter(CodingErrorAction.REPLACE)
* .decode(bb);
*
* except that it is potentially more efficient because it can cache
* decoders between successive invocations.
*
* This method always replaces malformed-input and unmappable-character
* sequences with this charset's default replacement byte array. In order
* to detect such sequences, use the {@link
* CharsetDecoder#decode(java.nio.ByteBuffer)} method directly.
*
* @param bb The byte buffer to be decoded
*
* @return A char buffer containing the decoded characters
*/
// public final CharBuffer decode(ByteBuffer bb) {
// try {
// return ThreadLocalCoders.decoderFor(this)
// .onMalformedInput(CodingErrorAction.REPLACE)
// .onUnmappableCharacter(CodingErrorAction.REPLACE)
// .decode(bb);
// } catch (CharacterCodingException x) {
// throw new Error(x); // Can't happen
// }
// }
/**
* Convenience method that encodes Unicode characters into bytes in this
* charset.
*
* An invocation of this method upon a charset cs returns the
* same result as the expression
*
*
* cs.newEncoder()
* .onMalformedInput(CodingErrorAction.REPLACE)
* .onUnmappableCharacter(CodingErrorAction.REPLACE)
* .encode(bb);
*
* except that it is potentially more efficient because it can cache
* encoders between successive invocations.
*
* This method always replaces malformed-input and unmappable-character
* sequences with this charset's default replacement string. In order to
* detect such sequences, use the {@link
* CharsetEncoder#encode(java.nio.CharBuffer)} method directly.
*
* @param cb The char buffer to be encoded
*
* @return A byte buffer containing the encoded characters
*/
// public final ByteBuffer encode(CharBuffer cb) {
// try {
// return ThreadLocalCoders.encoderFor(this)
// .onMalformedInput(CodingErrorAction.REPLACE)
// .onUnmappableCharacter(CodingErrorAction.REPLACE)
// .encode(cb);
// } catch (CharacterCodingException x) {
// throw new Error(x); // Can't happen
// }
// }
/**
* Convenience method that encodes a string into bytes in this charset.
*
* An invocation of this method upon a charset cs returns the
* same result as the expression
*
*
* cs.encode(CharBuffer.wrap(s));
*
* @param str The string to be encoded
*
* @return A byte buffer containing the encoded characters
*/
// public final ByteBuffer encode(String str) {
// return encode(CharBuffer.wrap(str));
// }
/**
* Compares this charset to another.
*
* Charsets are ordered by their canonical names, without regard to
* case.
*
* @param that
* The charset to which this charset is to be compared
*
* @return A negative integer, zero, or a positive integer as this charset
* is less than, equal to, or greater than the specified charset
*/
public final int compareTo(Charset that) {
return (name().compareToIgnoreCase(that.name()));
}
/**
* Computes a hashcode for this charset.
*
* @return An integer hashcode
*/
public final int hashCode() {
return name().hashCode();
}
/**
* Tells whether or not this object is equal to another.
*
* Two charsets are equal if, and only if, they have the same canonical
* names. A charset is never equal to any other type of object.
*
* @return true if, and only if, this charset is equal to the
* given object
*/
public final boolean equals(Object ob) {
if (!(ob instanceof Charset))
return false;
if (this == ob)
return true;
return name.equals(((Charset)ob).name());
}
/**
* Returns a string describing this charset.
*
* @return A string describing this charset
*/
public final String toString() {
return name();
}
}